The subject matter disclosed herein relates generally to photoacoustic imaging and, more specifically, to using photoacoustic tomography to characterize a target or targeted area within a tissue.
Moreover, the field of the invention relates generally to noninvasive imaging and, more particularly, to imaging an area with an object using confocal photoacoustic imaging.
Most living cells require oxygen to metabolize nutrients into usable energy. In vivo imaging of oxygen transport and consumption at high spatial and temporal resolution is required to understand the metabolism of cells and related functionalities. Although individual parameters such as sO2, partial oxygen pressure (pO2), or blood flow speed (Vflow) may partially characterize tissue oxygenation, no single parameter can provide a comprehensive view of oxygen transport and consumption. To quantify the fundamental metabolic rate of oxygen (MRO2), three primary imaging modalities have been employed in previous research: positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and diffuse optical tomography (DOT). These three imaging modalities are capable of imaging MRO2 at a millimeter-scale spatial resolution, but this resolution is inadequate to visualize MRO2 at a single-cell resolution, at which many important oxygen transport and delivery processes occur.
Photoacoustic (PA) microscopy has been proposed to measure MRO2 of a region at the feeding and draining blood vessels. However, this assessment of MRO2 has been limited to a relatively large region due to the limitations of existing PA microscopy devices. As a result, the feeding and draining blood vessels—especially those surrounding a tumor—may be numerous and difficult to identify. Since micrometer-sized RBCs are the fundamental elements for delivering most of the oxygen to cells and tissues, there exists a need for direct functional imaging of flowing individual RBCs in real time.
The capability of noninvasively imaging capillaries, the smallest blood vessels, in vivo has long been desired by biologists at least because it provides a window to study fundamental physiological phenomena, such as neurovascular coupling, on a microscopic level. Existing imaging modalities, however, are unable to simultaneously provide sensitivity, contrast, and spatial resolution sufficient to noninvasively image capillaries.